1. Field of the Invention
This invention relates to boat hulls, and more particularly concerns boat hulls made of laminated fiber reinforced plastic and with providing protection against blistering on the underwater surface of the boat hull.
2. Description of the Prior Art
Since the time when fiber reinforced plastic took over from wood as the major material used in the construction of boat hulls for pleasure marine craft, and many of the smaller work boats as well, the formation of blisters on the underwater hull surface has plagued designers, builders, and owners.
All synthetic resin plastic materials of boat hulls have a water vapor transmission rate when the lower or bottom surface is submerged in water while the upper surface of the hull is exposed to air. In a floating boat hull, the fiber reinforced plastic hull section of laminated layers below the water line of the boat gradually takes on a certain amount of water by osmosis.
The fiber reinforced plastic laminates of boat hulls contain certain amounts of water soluble molecules, some more than others. The chemical reaction which occurs when water soluble molecules of the hull have absorbed enough of the osmatic water may, in some instances, cause a sufficient localized parting of the hull laminated layers to form a blister on the outer surface of the hull.
If this blistering is sufficiently widespread on the underwater surface of the hull, it can seriously affect the performance of the boat. Left untreated, such blistered boat hulls continue to deteriorate, possibly even to the extent of creating a structurally unsound condition, so that the boat hull is not strong enough to be adequately covered by the designer's built-in safety factors.
As this problem became generally known to boat hull designers and builders, preventative measures were sought and tried. It became known that the most common plastic resin used in the plastic in fiber reinforced plastic boat hull construction was not the most resistant to moisture vapor transmission. However, many of its other properties continued to make it the most appealing product to the builders, and it is still the most widely used resin today in fiber reinforced plastic boat hull construction.
Listed below in the order of greatest resistance to moisture vapor transmission, are:
1. Epoxy PA1 2. Vinyl ester PA1 3. Isophthalic polyester resin PA1 4. DCPD polyester PA1 5. Orthophthalic polyester PA1 1. By using a specifically formulated outer gelcoat with a lower moisture vapor transmission rate than the standard isophthalic resin based outer gelcoat; PA1 2. Using a low moisture vapor transmission rate resin in the outer layer or layers of the laminate inside the gelcoat, normally a vinyl ester or a vinyl ester blend; PA1 3. Total use of high performance resin, as regards to moisture vapor transmission rate, in the laminate below the designed water line of the hull.
This listing, in reverse order, closely approximates the rating of the resin as regards total pounds of usage in the marine industry. Many laminated resins sold to boat builders by the resin producing industry are blends of two or more of the above resins.
Epoxy resins are difficult to use in the average boat hull production shop, being less tolerant of deviation from recommended procedures. Also, epoxy resins are considerably more expensive than the polyesters. The usage of epoxy resins is largely confined to high-tech specialty vessels using more exotic fabrics than the standard fiberglass and to parts requiring maximum strength with minimum weight. Epoxy resins are also used extensively in repairing damage to boat hulls and other parts of marine vessels.
Vinyl esters are used by many of the large boat manufacturers in combination with fiberglass as the bottom fiberglass-resin layer of the boat hull, next to the exterior finish coat which is known as a gelcoat, which gelcoat is usually a combination of an isophthalic polyester resin with pigment of a desired color. But vinyl esters are also demanding of a proper application technique. Vinyl esters are also considerably more expensive than various polyesters.
Isophthalic polyester resins are presently the preferred resin of choice for the outer gelcoat layer, as they produce a hard glossy surface which is desired for best cosmetics. They are not widely used otherwise, other than in combination with DCPD and orthophthalic polyester resin.
DCPD polyesters have come into common use in recent years, primarily by manufacturers of smaller boats. They give a good cosmetic appearance, and are easy to use, but are less flexible than the other resins. They normally are used in blends with orthophthalic and/or isophthalic resins, which are proprietary to the individual resin manufacturer. They usually are the least costly of all the marine resins.
Orthophthalic polyester resins have long been the choice for most manufactures in the marine field due to their user friendliness coupled with their low cost, good strength characteristics, and longer in-use history.
Builders have approached the hull bottom osmosis or blister problem in different ways:
While all of the above approaches may improve the resistance to hull blistering, none provides as significant improvement as does the present invention.
When a special gelcoat is used as the only agent for preventing blisters, it provides only a thin primary barrier, subject to cracks since it is more brittle than the other layers of the boat hull.
Even when using a resin, with a low moisture vapor transmission rate, in combination with fiberglass fibers, in all of the layers of the laminate, or in only the outer few layers, all of the layers of the laminate contain strands of glass fibers which can increase the moisture vapor transmission by a wicking action as well as contributing water soluble molecules to any water which penetrates the outer gelcoat.
In addition, the laminate lay-up process involves a hand rolling of the various layers, and it is not uncommon to have trapped air pockets occur directly behind the gelcoat which eventually become water reservoirs to react with the water soluble molecules in the laminate layers.
Reference is made to the following prior art patents which are incorporated herein by reference: U.S. Pat. No. 5,126,172 which issued on Jun. 30, 1992 on an application filed Nov. 20, 1990; U.S. Pat. No. 5,292,580 which issued on Mar. 8, 1994 which was filed on Jun. 30, 1992 and is a division of Ser. No. 616,239, filed Nov. 20, 1990, now U.S. Pat. No. 5,126,172; U.S. Pat. No. 5,277,145 which issued on Jan. 11, 1994 on an application filed Sep. 23, 1992, which is a continuation of Ser. No. 550,859, filed Jul. 10, 1990, abandoned; and U.S. Pat. No. 5,372,763 which issued on Dec. 13, 1994 on an application filed Jun. 30, 1993, which is a division of Ser. No. 950,968, filed Sep. 23, 1992, now U.S. Pat. No. 5,277,145.